The present invention is generally directed to carrier processes, and more specifically, to aggregation and coalescence processes for the preparation of carrier particles comprised, for example, of magnetic core particles and polymer particles as a coating. In embodiments, the present invention is directed to the economical in situ chemical preparation of carrier particles with, for example, a particle diameter of from about 20 to about 125, and preferably from about 20 to about 50 microns. The resulting carriers can be selected for known electrophotographic imaging and printing processes, including color processes, and lithography. In embodiments, the present invention is directed to a process comprised of mixing a magnetic pigment solution, especially a submicron magnetic solution and an ionic surfactant solution with a latex mixture comprised of suspended resin particles, preferably resin particles free of acrylic acid or optionally containing, for example, a maximum of about 1 pph of acrylic acid, where the latex particles are of a size in the range of 0.01 micron to about 1 micron in volume average diameter in an aqueous solution containing a counterionic surfactant in amounts of from about 1 percent to about 10 percent with opposite charge to the ionic surfactant of the pigment dispersion, and nonionic surfactant in an amount of from 0 percent to about 5 percent, followed by blending at speeds of about 3,000 to 5,000 rpm using a polytron, thereby causing a flocculation of the resin particles and pigment particles, followed by heating just below the resin Tg while stirring the resulting flocculent mixture to obtain aggregates of a size of from about 8 to 15 microns, and then gently heating the mixture, for example, in increments of 2.degree. to 3.degree. C. at a time at the rate of 0.25.degree. C. per minute, above the latex resin glass transition temperature (Tg), which Tg is in the range of from between about 45.degree. C. to about 100.degree. C. and preferably between about 50.degree. C. and about 90.degree. C., while monitoring the increase in particle size, and thereafter, adding in an effective amount of, for example, 0 to 70 milliliters of 20 percent (w/w of water) extra anionic or nonionic surfactant solution with a concentration of from about 5 percent to about 30 percent, which will result in an overall final concentration of this surfactant in the aggregated mixture of from about 0.5 percent to about 10 percent, and preferably from 1 percent to 5 percent (weight percent throughout unless otherwise indicated) to thereby enable any further growth in particle size during further heating, which size in embodiments is from about 20 to about 50 microns in average volume diameter; and more preferably the resin Tg is equal to 58.degree. C., to generate carrier with an average particle volume diameter of from about 20 to about 50 microns, and wherein in embodiments the stirring speed can be reduced from about 300 to about 1,000 to about 100, and preferably 150, to about 600 revolutions per minute to enable carrier particles comprised of magnetic particles encapsulated in, encased in, or coated with a polymer resin. In embodiments, the latex selected is synthesized by emulsion polymerization processes in an aqueous phase containing anionic and nonionic surfactants, and persulfate as an initiator. Thereafter, the resulting anionicly charged latex is mixed with a pigment solution containing the pigment magnetite at, for example, from about 40 to about 75 weight percent, and a cationic surfactant, such as alkylbenzyldimethyl ammonium chloride, and which mixture is polytroned at high speeds, for example from 5,000 to 10,000 revolutions per minute, to obtain a stable dispersion comprised of resin particles, pigment particles, water, anionic, nonionic, and cationic surfactants. Subsequently, the dispersion obtained is aggregated at a temperature of about 50.degree. C. or higher, for example in the range of from about 50 to about 70.degree. C. The aggregate size obtained when heated to 50 to 54.degree. C. is normally in the range of 8 to 12 microns with a narrow GSD, for example 1.24. The temperature is then gently raised above the resin Tg in increments of 2.degree. to 3.degree. C. in stages, and the particle size monitored. The particle size growth is accelerated when the temperature is raised above the resin Tg. As the temperature differential gets larger, the larger the particle size of the carrier. Upon approaching the desired particle size, there is added an anionic surfactant solution to primarily decrease and stop the growth of the aggregate particles when the temperature is further increased in the coalescence step. Without any or little, for example 0.5 pph, acrylic acid on the particle surface, the particles tend to grow and coalesce quicker and at a lower temperature as compared to aggregates containing acrylic acid. It is believed that during the second heating stage the components of aggregated particles fuse together to form carrier particles. Specifically, the carrier particles are prepared by first dispersing submicron magnetic particles, such as NP 604.TM., 608.TM., 628.TM.(from Northern Pigments), in an aqueous mixture containing a cationic surfactant, such as benzalkonium chloride (SANIZOL B-50.TM.), utilizing a high shearing device, such as a Brinkmann Polytron, or microfluidizer or sonicator, thereafter shearing this mixture with a charged latex of suspended resin particles, such as poly(styrene/butadiene/acrylic acid), poly(styrene/butylacrylate/acrylic acid) or PLIOTONE.TM. of poly(styrene butadiene), and of particle size ranging from about 0.01 to about 0.5 micron as measured by the Brookhaven nanosizer in an aqueous surfactant mixture containing an anionic surfactant, such as sodium dodecylbenzene sulfonate, for example NEOGEN R.TM. or NEOGEN SC.TM., and nonionic surfactant, such as alkyl phenoxy poly(ethylenoxy) ethanol, for example IGEPAL 897.TM. or ANTAROX 897.TM., thereby resulting in a flocculation, or heterocoagulation of the resin particles with the magnetic pigment particles; and which upon heating at from about 2.degree. to about 10.degree. C. below the resin Tg, which Tg is in the range of between 50.degree. to 90.degree. C. and preferably between about 55.degree. and 80.degree. C. and for a period of 1 to 6 hours and preferably for a period of 2 to 5 hours, results in formation of statically bound aggregates ranging in size of from about 8 microns to about 15 microns in average diameter size as measured by the Coulter Counter (Microsizer II) while stirring, the stirring in the range of 300 to 1,000 rpm and preferably in the range of 200 to 700 rpm. The temperature is further raised above the resin Tg in incremental steps of 2.degree. to 3.degree. C. and held for a period of at least 1 hour and preferably for a period of 0.5 hour while the particle size is monitored during every incremental step. The higher the temperature, the larger the particle size; and adding concentrated (from about 5 percent to about 30 percent) aqueous surfactant solution containing an anionic surfactant, such as sodium dodecylbenzene sulfonate, for example NEOGEN R.TM. or NEOGEN SC.TM., or nonionic surfactant, such as alkyl phenoxy poly(ethylenoxy) ethanol, for example IGEPAL 897.TM. or ANTAROX 897.TM., in controlled amounts (from about 5 percent to about 30 percent) to prevent any changes in particle size upon reaching the desired size, for example 30 microns to the mixture to prevent any growth of the aggregates. The temperature is further raised to 90.degree. C. to complete the coalescence of magnetic particles and resin, wherein the coalescence temperature is in the range of 75.degree. to 130.degree. C. and preferably in the range of 80.degree. to 120.degree. C., and wherein the carrier particle size obtained is in the range of 20 to 75 microns and preferably in the range of 25 to 60 microns with a narrow GSD of 1.26; followed by washing with, for example, hot water to remove surfactants, and drying whereby particles comprised of resin and magnetite of synthetic carrier particles are obtained.
Numerous processes are known for the preparation of carriers, for example solution and dry coating methods as illustrated in U.S. Pat. Nos. 4,937,166, and 4,935,326. In these methods, carrier core such as iron, or steel is heated with a polymer coating, or coatings until adherence of the coating to the core.
There is illustrated in U.S. Pat. No. 4,996,127 a toner of associated particles of secondary particles comprising primary particles of a polymer having acidic or basic polar groups, and a coloring agent. The polymers selected for the toners of this '127 patent can be prepared by an emulsion polymerization method, see for example columns 4 and 5 of this patent. In column 7 of this '127 patent, it is indicated that the toner can be prepared by mixing the required amount of coloring agent and optional charge additive with an emulsion of the polymer having an acidic or basic polar group obtained by emulsion polymerization. Also, note column 9, lines 50 to 55, wherein a polar monomer, such as acrylic acid, in the emulsion resin is necessary, and toner preparation is not obtained without the use, for example, of an acrylic acid polar group, see Comparative Example I. The aforementioned patent does not disclose the preparation of carrier particles. In U.S. Pat. No. 4,983,488, there is illustrated a process for the preparation of toners by the polymerization of a polymerizable monomer dispersed by emulsification in the presence of a colorant and/or a magnetic powder to prepare a principal resin component, and then effecting coagulation of the resulting polymerization liquid in such a manner that the particles in the liquid after coagulation have diameters suitable for a toner. It is indicated in column 9 of this patent that coagulated particles of 1 to 100, and particularly 3 to 70 are obtained. This process is thus primarily directed to the use of coagulants, such as inorganic magnesium sulfate which results in the formation of particles with wide GSD. The aforementioned patent does not disclose the preparation of synthetic carrier particles.
In U.S. Pat. No. 5,403,693, there is illustrated a process for the preparation of toner compositions with controlled particle size comprising:
(i) preparing a pigment dispersion in water, which dispersion is comprised of a pigment, an ionic surfactant in amounts of from about 0.5 to about 10 percent by weight of water, and an optional charge control agent;
(ii) shearing the pigment dispersion with a latex mixture comprised of a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant, a nonionic surfactant, and resin particles, thereby causing a flocculation or heterocoagulation of the formed particles of pigment, resin, and charge control agent;
(iii) stirring the resulting sheared viscous mixture of (ii) at from about 300 to about 1,000 revolutions per minute to form electrostatically bound substantially stable toner size aggregates with a narrow particle size distribution;
(iv) reducing the stirring speed in (iii) to from about 100 to about 600 revolutions per minute, and subsequently adding further anionic or nonionic surfactant in the range of from about 0.1 to about 10 percent by weight of water to control, prevent, or minimize further growth or enlargement of the particles in the coalescence step (iii); and
(v) heating and coalescing from about 5.degree. to about 50.degree. C. above about the resin glass transition temperature, Tg, which resin Tg is from between about 45.degree. C. to about 90.degree. C. and preferably from between about 50.degree. C. and about 80.degree. C., the statically bound aggregated particles to form said toner composition comprised of resin, pigment and optional charge control agent.
Emulsion/aggregation processes for the preparation of toners are illustrated in a number of Xerox patents, the disclosures of which are totally incorporated herein by reference, such as U.S. Pat. No. 5,290,654, U.S. Pat. No. 5,278,020, U.S. Pat. No. 5,308,734, U.S. Pat. No. 5,346,797, U.S. Pat. No. 5,370,963, U.S. Pat. No. 5,344,738, U.S. Pat. No. 5,403,693, U.S. Pat. No. 5,418,108, U.S. Pat. No. 5,364,729, and U.S. Pat. No. 5,346,797.